I want to see gaps in my bar chart where there is no data for every day. My original data does not have these zero values - it only has rows where something happened on that day. I have tried checking 'Show null values' but this doesn't seem to make a difference.

If it has any implication, I have created the date dimension using MakeDate(Year,Month,Day) because my original data had individual columns for day, month and year.

I am not sure how this could be done in QlikSense, but in QlikView I would just create a Master Calendar with all dates and use that as date instead of using MakeDate in the front end. By using make date you are essentially creating only those dates which are available in your fact table. To create dates which doesn't have a value you will have to add some kind of master calendar.

the code from my qvw will not help you to solve your issue out of the box. All it does showing principly how to create a gapless calender and link it to a given datamodell. In this example the datamodell is just one table (_Data).

If you do this in your app analog to what I've shown in my example you should be able to get a barchart showing the gaps as well. This works as well in QlikSense.